Neo-Sapien theme: how to restore original font color of post/page text

This issue is keeping me up for quite sometime already. I'm bewildered why the text color of my post turned into gray (almost unreadable because the background is a slightly lighter shade of gray). I was just editing tags and added a page, then suddenly all my texts are gray.

I didn't purchase the custom CSS. I wonder why the font color has changed.

Can you tell me how to restore the original font color (black)? I would appreciate your help a lot. Thanks so much!